<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>大盒子套着小盒子</title>
		<style>
			#main{
				width: 800px;
				height: 500px;
				border: 1px solid red;
			}
			#main div{
				height: 100px;
				width: 400px;
				background-color: darkcyan;
				margin: 5px;
			}
			#main .c3{
				position: absolute;
				left: 0;
				top: 0;
				width:450px ;
				background-color: red;
			}
		</style>
	</head>
	<body>
		<div id="head" style="height: 120px;border: 4px solid green;"></div>
		<div id="main">
			<div>1</div>
			<div>2</div>
			<div class="c3">3</div>
			<div>4</div>
		</div>
	</body>
</html>
